This invention relates to a process for preparing an 2-alkyl-2-adamantyl ester such as 2-alkyl-2-adamantyl acrylates and 2-alkyl-2-adamantyl methacrylates (hereinafter, collectively referred to as 2-alkyl-2-adamantyl (meth)acrylates), which are useful as a material for producing a semiconductor resist.
A resist prepared from an 2-alkyl-2-adamantyl ester as a starting material has been known to be highly resistant to dry etching during a process for producing a semiconductor (see, e.g., JP-A 5-265212), and has been thus expected to be a promising resist for a semiconductor.
A known process for preparing an 2-alkyl-2-adamantyl ester involves alkylating 2-adamantanone using an alkylating agent consisting of an organometallic compound, and then esterifying the resulting metal 2-alkyl-2-adamantyl alcoholate with an acid halide (e.g., JP-A 10-182552).
In the first alkylation step in the above reaction, when the alkylating reagent is an organomagnesium or organoaluminum compound, a reduction reaction preferentially proceeds, leading to a reduced yield of the alkyl compound as described in, e.g., Tetrahedron Lett., Vol. 31 (22), p. 3151 (1990). Thus, a desired ester may be obtained in a significantly lower yield.
For example, as described in Comparative Examples later, selectivities for an alkylated product (an ethylated compound) and a reduced product (2-adamantanol) were 25% and 75%, respectively, in a reaction of 2-adamantanone with ethylmagnesium iodide. As a result, a reaction yield of the ester was significantly low, i.e., about 20% based on 2-adamantanone. In the reaction, a lower content of the ester makes its purification very difficult. Thus, the ester with a high purity cannot be obtained using a common purification method.
In general, alkylation using an alkyllithium as an alkylating reagent may frequently eliminate a reduction reaction as described above, allowing the above problem to be solved. An alkyllithium itself may be, however, prepared in a lower yield and has a short half life as indicated in J. Am. Chem. Soc., Vol. 63, p. 2480 (1941) describing that ethyl lithium is prepared from ethyl bromide and lithium metal in an yield of at most about 50%, and in xe2x80x9cYuki Kagaku Jikken No Tebiki (Guide for Organic Chemical Experiments), Kagaku Dojin, p. 34 (1988) describing that ethyl lithium has a half life as short as 54 hours. Thus, the reagent is expensive and unstable.
Alkylation with an alkyllithium is, therefore, not unfavorable due to its higher production cost and troublesome operation in the light of the overall production process. Thus, the yield in the first alkylation step also significantly affects the yield of the ester.
On the other hand, there have been known the conditions under which the second esterification step may stoichiometrically proceed, particularly when the metal is lithium. However, when using acryloyl chloride or methacryloyl chloride (hereinafter, acrylic and methacrylic acids are collectively referred to as (meth)acrylic acid) as an acid halide for esterification of a metal 2-alkyl-2-adamantyl alcoholate prepared by alkylation of 2-adamantanone, an ester produced is polymerized during the reaction, resulting in a reduced overall yield.
A resist material for a semiconductor must be highly pure. Conventional processes for preparing an 2-alkyl-2-adamantyl ester, therefore, carry industrially serious problems in terms of a lower yield and difficulty in purification.
We have extensively investigated processes for preparing an 2-alkyl-2-adamantyl (meth)acrylate by reacting lithium 2-alkyl-2-adamantyl alcoholate with (meth)acryloyl chloride, and have found that an xe2x80x94OLi group in an lithium 2-alkyl-2-adamantyl alcoholate polymerizes 2-alkyl-2-adamantyl (meth)acrylate produced by the reaction.
In addition, we have found that when a solution of lithium 2-alkyl-2-adamantyl alcoholate is added to (meth)acryloyl chloride, polymerization of the 2-alkyl-2-adamantyl(meth)acrylate can be prevented.
Furthermore, we have intensely investigated alkylation of 2-adamantanone and have found that 2-adamantanone can be alkylated by reacting 2-adamantanone, lithium metal and an alkyl halide instead of using an unstable alkyllithium described above. We have also found that a solution containing 2-adamantanone and alkyl halide can be slowly added to lithium metal to alkylate 2-adamantanone more effectively, and that the alkylation reaction gives a highly pure product and thus a resulting solution can be directly used in the subsequent esterification without further isolation to give a highly pure product after isolation. Thus, this invention has been achieved on the basis of these findings.
Thus, an objective of this invention is to provide a process for preparing an 2-alkyl-2-adamantyl ester with a high purity in an improved yield from 2-adamantanone without using an expensive and unstable compound such as an alkyl lithium.
Another objective of this invention is to provide a process for preparing an 2-alkyl-2-adamantyl ester whereby the ester can be produced in a high yield by preventing the ester from polymerizing during esterification of a metal 2-alkyl-2-adamantyl alcoholate with an acid halide.
For realizing the above objectives, this invention provides:
[1] A process for preparing an 2-alkyl-2-adamantyl (meth)acrylate comprising the step of adding a solution of a lithium 2-alkyl-2-adamantyl alcoholate to a (meth)acryloyl halide to react the lithium 2-alkyl-2-adamantyl alcoholate with the (meth)acryloyl halide.
[2] The process for preparing an 2-alkyl-2-adamantyl (meth)acrylate as described in [1] wherein the solution of the lithium 2-alkyl-2-adamantyl alcoholate is prepared by combining a solution or suspension containing 2-adamantanone and an alkyl halide with lithium metal.
[3] The process for preparing an 2-alkyl-2-adamantyl (meth)acrylate as described in [1] wherein the alkyl is alkyl having 1 to 6 carbon atoms.
[4] The process for preparing an 2-alkyl-2-adamantyl (meth)acrylate as described in [1] wherein the alkyl is ethyl.
In this invention, a solution or suspension of 2-adamantanone and an alkyl halide is reacted with lithium metal to prepare a solution of an lithium 2-alkyl-2-adamantyl alcoholate. The lithium 2-alkyl-2-adamantyl alcoholate can be, therefore, prepared in a high yield and furthermore, the resulting alcoholate is reacted with an acid halide to give a desired product, an 2-alkyl-2-adamantyl ester in a high yield.
The lithium 2-alkyl-2-adamantyl alcoholate can be prepared in a high yield when a solution or suspension of 2-adamantanone and an alkyl halide is added to lithium metal. Furthermore, when the solution of the lithium 2-alkyl-2-adamantyl alcoholate thus prepared is added to an esterifying agent or its solution, the desired product, 2-alkyl-2-adamantyl (meth)acrylate, is prevented from polymerizing. As a result, the yield of the desired product is improved. Furthermore, a reduced amount of impurities in the desired product makes a purification process easier and thus the desired product can be obtained easier with a high purity.
According to the preparation process of this invention, a desired product can be obtained in a higher yield than a process using a Grignard reagent. In addition, since the process does not use an alkyllithium which must be separately prepared and is unstable, an adamantyl ester can be easily prepared with a lower cost.
Preparation of a Lithium 2-alkyl-2-adamantyl Alcoholate
As described above, in the first step of the process according to this invention, a solution or suspension of 2-adamantanone represented by formula (1) and an alkyl halide represented by formula (2): xe2x80x83R1-Xxe2x80x83xe2x80x83(2)
wherein R represents alkyl having 1 to 6 carbon atoms and X represents halogen, is combined with lithium metal for initiating alkylation of 2-adamantanone to prepare a lithium 2-alkyl-2-adamantyl alcoholate represented by formula (3): 
wherein R1 represents alkyl having 1 to 6 carbon atoms.
One starting material, 2-adamantanone is commercially available as a reagent or industrial grade, which may be used as it is or after purification by, for example, recrystallization or sublimation.
The other starting material, an alkyl halide (2), may be selected from, but not limited to, alkyl bromides, alkyl iodides and alkyl chlorides. In the light of availability of the starting material, preferred are alkyl bromides and iodides having 1 to 6 carbon atoms. Specific examples include butyl chloride, pentyl chloride, hexyl chloride, methyl bromide, ethyl bromide, butyl bromide, methyl iodide and ethyl iodide.
The amount of the alkyl halide is desirably 2-adamantanone:alkyl halide=1:1 to 1:1.2 in a molar ratio, taking a high conversion rate of 2-adamantanone into account.
A solvent or dispersion medium which dissolves or disperses 2-adamantanone and the alkyl halide may be an organic solvent which is stable to lithium metal, an alkyllithium and a lithium alcoholate. Examples of such an organic solvent include ethers such as diethyl ether, dioxane and tetrahydrofuran; hydrocarbons such as hexane and toluene; and mixtures thereof.
Such an organic solvent is preferably used in an amount such that the concentration of 2-adamantanone is 0.01 to 10 mol/L, particularly 0.1 to 5 mol/L in the light of a crude yield, solubility and a reaction rate, but not limited to the range.
The total amount of lithium metal is preferably, but not limited to, 1.6 to 2.4 gram atom, particularly 1.8 to 2.2 gram atom per 1 mole of adamantanone in the light of an yield and avoiding excessive use of lithium metal.
When subsequently conducting the esterification reaction described below, it is preferable that lithium metal in the reaction solution and the alkyllithium generated in the reaction system are substantially absent after the alkylation. The amount of lithium metal is, therefore, preferably 2 gram atom or less, particularly 1.8 to 2.0 gram atom per 1 mole of 2-adamantanone.
There are no restrictions to a procedure of the reaction initiated by combining a solution or suspension (an organic material mixture) of 2-adamantanone and an alkyl halide with lithium metal. Specifically, in terms of the order of addition, the organic material mixture may be added to lithium metal or lithium metal may be added to the organic material mixture. In terms of a mixing procedure, these materials may be mixed together at a time, successively or continuously.
Among these mixing procedures, addition of an organic material mixture to lithium metal is particularly preferable because it can prevent lithium metal from being inactivated, increase a reaction rate and prevent lithium metal from remaining at the end of the reaction. In the procedure, to lithium metal is added an organic material mixture portionwise over a relatively longer period, or dropwise continuously or intermittently while controlling a reaction temperature within the range described later.
In contrast, when adding lithium metal portionwise to an organic material mixture, a time for activating a metal surface is required after adding each aliquot of lithium metal. Thus, the overall reaction proceeds in a lower rate. However, in the mixing procedure of adding the organic material mixture to lithium metal, the whole amount of lithium metal used can be activated during an initial stage of the reaction so that the reaction may be quite smooth.
A time for adding the organic material mixture to lithium metal may vary depending on a production scale, but is preferably 0.5 to 48 hours.
Lithium metal may be used preferably as granules, foils or particles having a large surface area which can accelerate the reaction.
A rate of adding the organic material mixture cannot be particularly defined because it varies depending on the type of an alkyl halide used. Generally, it is desirable to adjust an addition rate such that a reaction temperature does not exceed a lower temperature of a boiling point of the alkyl halide or a boiling point of the organic solvent used.
In particular, when the alkyl halide is an iodide, it is desirable to add an organic material mixture while maintaining a reaction temperature to 0xc2x0 C. or lower in the light of minimizing side reactions. When the alkyl halide is a bromide, it is desirable to add an organic material mixture to lithium metal while maintaining a reaction temperature to a level not only meeting the above conditions but also equal to or exceeding 20xc2x0 C., that is, 20xc2x0 C. to a lower tempeature of a boiling point of the alkyl halide or a boiling point of the organic solvent used. Conducting such adjustment may prevent inactivation of lithium metal. During adding the organic material mixture is preferably added to lithium while stirring the solvent.
A reaction time for the above alkylation may vary depending on factors such as the amount of lithium metal used and a cooling efficiency, but is preferably 0.5 to 10 hours after adding an organic material mixture. The reaction is desirably conducted in an inert atmosphere such as argon for preventing inactivation of lithium metal.
Esterification
In the process for preparing an 2-alkyl-2-adamantyl ester according to this invention, an 2-alkyl-2-adamantyl alcoholate prepared by the above alkylation is reacted with an acid halide to prepare the 2-alkyl-2-adamantyl ester.
One starting material in the esterification, an 2-alkyl-2-adamantyl alcohol may be used as a lithium 2-alkyl-2-adamantyl alcoholate as prepared above without being isolated. Alternatively, a lithium 2-alkyl-2-adamantyl alcoholate may be separated and if necessary purified before being used in a subsequent reaction.
When separating the lithium 2-alkyl-2-adamantyl alcoholate from a reaction solution, the lithium 2-alkyl-2-adamantyl alcoholate itself may be not necessarily isolated. If possible, the above alcoholate may be separated from the remaining lithium metal while being dissolved in the solution. When the reaction solution after the above alkylation does not substantially contain lithium metal, the reaction solution may be used directly as a material for esterification.
If the reaction solution is used as a material for esterification while containing lithium metal or an alkyllithium remains in a large amount, it may cause inactivation of an acid halide or polymerization of an 2-alkyladamantyl ester produced, leading to reduction in an yield of the desired 2-alkyladamantyl ester.
An acid halide of the other starting material used in the esterification is not limited as long as it corresponds to the structure of a desired product. Halogens which can be shown include chlorine, bromine and iodine. Chlorine is preferable because it can readily prepare an acid halide.
Examples of an acid halide which can be used in the esterification include acetyl chloride, acetyl bromide, acryloyl chloride, methacryloyl chloride, benzoyl chloride and 4-vinylbenzoyl chloride.
Among these, an acryloyl or methacryloyl halide, particularly acryloyl or methacryloyl chloride, is preferable as a starting material for an alkyladamantyl ester which is very useful as a resist.
In the esterification, the amount of a lithium 2-alkyl-2-adamantyl alcoholate and an acid halide is preferably 0.9 to 2.0 moles of an acid halide per 1 mole of a lithium 2-alkyl-2-adamantyl alcoholate, more preferably 1.0 to 1.3 moles because an yield may be improved.
The above esterification may be initiated by contacting the lithium 2-alkyl-2-adamantyl alcoholate with the acid halide in a solvent.
Any solvent may be used as long as it does not react with an alcoholate or an esterifying agent. Examples of such a solvent include ethers such as ethyl ether, tetrahydrofuran (THF) and dioxane; and hydrocarbons such as hexane, toluene and xylenes.
A concentration of an lithium 2-alkyl-2-adamantyl alcoholate in the above solvent is preferably 0.01 to 10 mol/L, more preferably 0.1 to 1 mol/L in the light of handling.
There are no restrictions to a procedure of contacting a lithium 2-alkyl-2-adamantyl alcoholate with an acid halide in a solvent. They may be combined by adding a lithium 2-alkyl-2-adamantyl alcoholate (or its solution) and an acid halide (or its solution) simultaneously and separately to a solvent; by adding an acid halide (or its solution) to a solution of a lithium 2-alkyl-2-adamantyl alcoholate; or by adding a lithium 2-alkyl-2-adamantyl alcoholate (or its solution) to a solution of an acid halide.
A particularly preferable procedure of contacting an lithium 2-alkyl-2-adamantyl alcoholate with an acid halide in a solvent is as follows. A solution of the lithium 2-alkyl-2-adamantyl alcoholate is added to the acid halide or its solution to initiate an esterification reaction by which an 2-alkyl-2-adamantyl (meth)acrylate is produced.
The above contacting procedure can effectively prevent the 2-alkyl-2-adamantyl (meth)acrylate produced during the reaction from polymerizing due to the presence of the xe2x80x94OLi group in the lithium 2-alkyl-2-adamantyl alcoholate, resulting in improvement in an yield of the desired product. Such an effect is particularly prominent when the acid halide is an acryloyl halide or methacryloyl halide.
When adding a solution of the lithium 2-alkyl-2-adamantyl alcoholate to an acid halide or its solution, it may be preferable to continuously or intermittently add dropwise the solution of the lithium 2-alkyl-2-adamantyl alcoholate to the acid halide or its solution over a relatively longer period while maintaining a reaction temperature within the range described below. A dropping period may be, therefore, often about 1 to 48 hours although it depends on a production scale.
Depending on a dropping period, a reaction time is preferably 0.5 to 10 hours after completion of addition.
A reaction temperature in the esterification may not be particularly restricted, but is preferably xe2x88x9220 to 100xc2x0 C., particularly preferably xe2x88x9220 to 50xc2x0 C. in the light of balance between a reaction rate and prevention of polymerization.
The reaction is desirably conducted in an atmosphere of an inert gas such as nitrogen and argon for preventing inactivation of an acid halide or a lithium 2-alkyl-2-adamantyl alcoholate.
The reaction system may contain a polymerization inhibitor unreactive to a lithium alkoxide. Examples of such a polymerization inhibitor include those without a phenolic hydroxyl group such as phenothiazine.
Esterification can be conducted as described above to obtain a desired alkyladamantyl ester by using corresponding to an alkyl halide and an acid halide used. For example, when using an alkyl halide comprising alkyl having 1 to 6 carbon atoms as an alkyl halide and an acryloyl or methacryloyl halide as an acid halide, an alkyladamantyl (meth)acrylate represented by formula (4) can be obtained. 
wherein R1 represents alkyl having 1 to 6 carbon atoms; and R2 represents hydrogen or methyl.
A desired product may be obtained from a reaction solution after esterification, by removing a lithium halide as a byproduct by an appropriate procedure such as washing with water, removing a solvent, and then purifying it by a proper method such as column chromatography, distillation and recrystallization.